Field of the Invention
The present invention related to an apparatus and a method for checking an inclination of a cushion pad, and more particularly to an art of properly and efficiently performing shim adjustment in a die cushion device.
Description of the Related Art
FIGS. 15A and 15B are schematic views each of which illustrates a press machine provided with a die cushion device, and which illustrate a state before starting press forming and a state during the press forming, respectively. An upper die 120 is attached to a lower face of a slide 104 of the press machine, and a lower die 122 is attached to an upper face of a bolster 108. When pressing forming material, the press machine lowers the slide 104 to perform forming of the material between the upper die 120 and the lower die 122.
The die cushion device applies die cushion force to a cushion pad 202 (or the blank holder 206) during a die cushion stroke from a die cushion standby position to press bottom dead center in a state where the upper die 120 and the lower die 122 (a blank holder 206) are in close contact (or contact by surface not only point) with each other through the material.
In general, each of the slide 104 and the bolster 108 of the press machine is configured to be horizontal. In addition, in a state where the cushion pad 202 is held at the standby position, a flat face of the cushion pad 202 (blank holder 206 supported through cushion pins 208) is set so as to be parallel to the slide 104 (a flat face to which the upper die 120 is attached) of the press machine.
In the press machine configured as above, when a defective product occurs during forming with a die for which the die cushion device is used or when a product is preliminarily formed, a shim (a spacer) is sometimes inserted into the die for adjustment (shim adjustment) as a correction method for forming a non-defective product.
FIGS. 15A and 15B illustrate a case where a shim 207 with desired thickness is inserted into a shim adjustment position on the blank holder 206 (a shim adjustment position on the left side of the blank holder 206 in FIGS. 15A and 15B).
If the shim adjustment is performed, the upper die 120 and the blank holder 206 are not parallel to each other, and as illustrated in FIG. 15B, when the upper die 120 and the blank holder 206 are brought into close contact (or contact by surface not only point) with each other during forming, the cushion pad 202 is inclined by the blank holder 206 through the cushion pins 208.
When a state where the cushion pad 202 is held at the horizontal die cushion standby position as illustrated in FIG. 15A changes to a state where die cushion force control is performed as illustrated in FIG. 15B, the cushion pad 202 is inclined as the blank holder 206 is inclined by the shim adjustment, and is particularly inclined rapidly at the moment when control of die cushion force is started (when the upper die and the lower die collide with each other). Then, at the time when the control of die cushion force is started as illustrated in FIG. 15B (at the time of collision), a large difference in die cushion force between the right and left sides of the cushion pad 202 occurs to cause stability of the control of die cushion force to be impaired, whereby the die cushion force is asymmetrical between the right and left sides. The difference in the die cushion force on the right and left sides may cause material to be broken or may have an adverse effect on formability (particularly formability on the left side lagging in operation) to cause unevenness force in a plane to occur, whereby it is not favorable for forming.
Heretofore, in order to solve the problem above, there is provided a die cushion device in which information on an inclination of the cushion pad 202 during forming are detected by a plurality of die cushion position detection device so that a cushion pad is caused to wait so as to be parallel to a lower face of an upper die attached to a slide at a die cushion standby position (Patent Literature 1: Japanese Patent Application Laid-Open No. 2014-140871).